I am reaching out here because our client had a question and I had no answer for it.
Here is our case: We have a fairly large schedule (7000 activities) in P6 and we did duration uncertainty ranging for 454 activities near to critical path (TF<2weeks) also remaining duration more than 2 weeks.
Project duration is 2.5 years.
Results off of PRA risk analysis show 50% and 80% are only a week apart. Now client says that they use to see at least a month difference between P50 and P80.
More than likely due to nodal bias... or as I call it.. car pool syndrome. I imagine you have several parallel tasks all independent.. so does not matter which one is late, the successor starts late. Try this as an exercise... Correlate all your uncertainties 100%. Run the risk analysis again... If you have a much wider spread then question which tasks should be correlated.... For example should all Engineering electrical design be as same contractor... are the pipeline construction activities being carried out by same EPC.